Rigid working substrates of glass and other similar silicone materials are used extensively in certain steps in the preparation of printed circuits. Integrated circuit patterns are transposed onto such substrates and then transposed photographically onto silicone wafers for division and application to printed circuit boards. The completion of such printed circuitry always requires a multi-step procedure, and accordingly, the substrates must be handled, and oftentimes shipped from one plant to another, during the processing of the printed circuits.
Because the substrates are rather large in dimension and of small thickness, the likelihood of breakage of such substrates, especially during shipping, is rather high. It should be recognized that substrates of this type used as the structural base for printed circuits are oftentimes square with a width of two to six inches. The thickness of such substrates is oftentimes within the range of 60 to 250 thousandths of an inch.
No devices have been previously known which are satisfactory for the purpose of retaining and cushioning such substrates confined in shipping containers to avoid movement of the substrates in the shipping containers and to avoid the possibility of breakage of the substrates.
Previously, a simple resilient pad has been used between the top edge of the substrate and the lid of the shipping container. Such pads of flexible polyurethane foam confined in a polyethylene bag have proven to be quite unsatisfactory. The pad and the bag have been cut to shreds by the sharp edges of the substrates; the pad is not reusable; the particles from the pad when cut or shredded by the substrates falls down onto the substrates in the shipping container and contaminates these substrates, requiring further cleaning; and the glass substrates have simply not been adequately retained in the shipping container, and it has been found that when one substrate breaks, numerous other adjacent substrates also break by domino effect of one substrate acting upon the next in the container.